When should I rotoscope in the compositting proces?
When to rotoscope?
Whenever you need to evaluate the integration of the video element you want to composite.
Can rotoscoping be done in blender?
Yes.
You can draw and animate masks that can be used in the compositor. Mask drawing tools are quite robust in blender, allowing you to add, subtrac or intersect different masks and layers, and it allows you to create sharp or feathered edges.
Advanced and semi-automated rotoscoping can be done by parenting masks to tracking points on the video clip editor.